The present invention relates to novel and unique catalyst systems comprising catalyst particles, a method for preparing same, the use of the catalyst particles for polymerization reactions and methods of controlling the catalyst particle morphology.
Catalyst systems comprise catalysts, which include one or more catalyst components and optionally cocatalysts, external donors and poison scavengers or any other catalyst additives. Catalysts which are solutions of one or more catalyst components are known in the field as homogeneous catalysts. Typically, homogeneous catalysts and catalyst systems are used as liquids in the polymerization process. Such systems have in general a satisfactory catalytic activity, but their problem has been that the polymer thus produced has a poor morphology. As a consequence, operation of slurry and gas reactors using a homogeneous catalyst system caused problems in practice, since for example fouling of the reactor can occur.
Various approaches have been attempted in order to overcome this drawback. Homogeneous catalysts, for example, have been subjected to prepolymerization in order to introduce the catalysts or catalyst systems in the form of prepolymerized polymer particles comprising catalytically active sites into polymerisation reactions. Other attempts have been made in order to support the homogeneous catalyst on carrier materials, such as solution impregnation methods on porous organic and inorganic support materials, such as silica, MgCl2, or porous polymeric materials. Such kinds of heterogeneous supported catalyst systems are widely used e.g. in the field of olefin polymerisations.
The international present application WO 2004/089542, for example, discloses the use of porous functionalized beads of polystyrene in order to immobilize an iron based polymerization catalyst.
However, also supported catalysts present drawbacks. It is often difficult to get an even distribution of the catalyst components within the porous carrier material. Furthermore, it is possible that the catalyst components are leached from the support, so that overall unsatisfactory polymerization behavior of the catalyst occurs. Carrier materials furthermore can also have adverse effects on the activity of the catalyst, the polymerization behavior and the properties of the polymeric product.
Accordingly, there exists the need in the art to provide alternative and improved ways of employing heterogeneous catalysts and catalyst systems for polymerization reactions which do not suffer from the drawbacks as identified above.